This invention relates generally to cellulosic animal litters and, more particularly, to clumping cellulosic animal litters made from specially treated agglomerated cellulosic particles.
Small domesticated animals, such as cats, are often trained to urinate and defecate in special containers commonly referred to as litter boxes. Untrained caged animals, such as guinea pigs, hamsters, gerbils, dogs, birds, monkeys, ferrets and laboratory mice and rats urinate and defecate on the floors of their cages. Therefore, pet owners, veterinarians and laboratory personnel line the bottoms of litter boxes and cages with absorbent material to collect the animals"" urine and feces. In order to control objectionable odors from the contaminated absorbent material, it is necessary to periodically remove and dispose of that material and to replace it with fresh absorbent material.
Until recently, it was found to be necessary to completely remove contaminated absorbent material from the litter boxes and cages in order to control objectionable odors. However, now, clay-based absorbent materials have been developed which, when wetted with animal urine, form coherent clumps that may be easily segregated and removed from the remaining uncontaminated absorbent material. These clay-based absorbents, which are generally referred to as xe2x80x9cclumping littersxe2x80x9d, are more efficient and convenient to use than prior absorbent materials. As a result, they have gained widespread commercial acceptance.
Unfortunately, clay-based absorbents have some drawbacks. First, they are dusty. Second, clump formation in clay-based clumping litters is often not as rapid as would be desired. Also, the clumps are often soft and friable, which can complicate the removal of the wetted clumps. Additionally, clay-based clumping litters are relatively expensive since they require that the clay be mined, processed, and often shipped long distances. The mining process is not only expensive, it can scar the landscape and is therefore environmentally undesirable. Also, different types of clay must be combined and treated in certain ways in order to achieve the desired clumping effect.
Substrates containing at least 10% by weight cellulosic content are a known alternative to straight clay-based absorbents for use in absorbing and disposing of animal urine and feces. When such cellulosic materials are made from waste produced in paper manufacture, they offer significant advantages over clay-based absorbents. First, the starting material is very inexpensive. Second, it is plentifully available and, once used and disposed of, the cellulosic component readily degrades, reducing the disposal problems inherent in the use of clay-based absorbents. Some particularly desirable methods of making cellulosic granules from paper waste are described in U.S. Pat. Nos. 4,560,527, 4,619,862, 4,621,011, and 4,721,059, the disclosures of which are incorporated herein by reference.
Although untreated cellulosic granules may form friable clumps, until the advent of the present invention, the only practical method for making reliable and efficient clumping cellulosic absorbents is described in U.S. Pat. No. 5,970,916 to the present inventors. This patent describes a cellulosic animal litter in which the cellulosic particles which make up the litter are coated first with xanthan gum and then with guar gum. Although the clumping cellulosic litter of the ""916 patent works well, it is desirable to improve the performance and reduce the costs of making a clumping cellulosic litter.
Since the development of the invention described in U.S. Pat. No. 5,970,916, the present inventors have come to recognize that it is essential to form clumps of urine-soaked litter immediately as the litter is wetted. Otherwise, since cats instinctively scratch and dig into the litter to cover their wastes, they often spread the litter before it is able to form clumps, thereby reducing the overall efficiency and convenience of using clumping litter.
This problem is addressed in the present invention in which near instantaneous clumping is achieved. The present invention thus constitutes an important contribution to the animal litter art.
The present invention represents a substantial advance in clumping cellulosic absorbents by providing coated cellulosic particles having a first or inner coating of a dual adhesive and surface active agent and a second or outer coating of guar gum. The dual adhesive and surface active agent must be: 1) water soluble, 2) capable of penetrating and drying into the particulate cellulosic absorbents, 3) capable of adhering to guar, and 4) capable of being readily re-solubilized when the granule is wetted with urine. Also, a mixture of coated and uncoated particulate cellulosic absorbents may be used.
Certain polyacrylates have been identified which satisfy the above requirements, as will described below. Since the properties of polyacrylates in respect of these properties is not strictly predictable, it is expected that other polyacrylates as well as acrylate copolymers (e.g., methyl methacrylate) could also be used. Such acrylates and polyacrylates will have to be identified by routine testing against the above criteria, performed by those of ordinary skill in the polymer art.
The polyacrylates already known to perform as a dual adhesive and surface active agent in the practice of this invention will have an average molecular weight of about 1000 to 5000, with an average molecular weight of about 2000 to 4000 being preferred, and an average molecular weight of about 2000 to 3000 being presently most preferred. A specific polyacrylate that has been found to be particularly useful as a dual adhesive and surface active agent is sold under the designation Spinks 211 by H.C. Spinks Clay Company, Inc., of Paris, Tenn. Spinks 211 is an aqueous sodium polyacrylate solution. It is a clear, amber fluid, with a solids content (% by weight, dry 0.6 gram at 150xc2x0 C. for 60 minutes in a forced draft oven) of 43.0-45.0, a pH (ASTM E-70) of 7.00-8.00, and a viscosity (as shipped, cps Brookfield LV spindle #2, 30 rpm, 25xc2x0 C.) of 100-500. Spinks 211 has an average molecular weight of about 2000-3000.
The amount of dual adhesive and surface active agent used will be at least an amount sufficient to coat 50% of the surface of the granules and no more than the amount capable of being absorbed by the granule. Preferably, the dual adhesive and surface active agent will be present in an amount that primarily coats and only minimally penetrates into the granules. The actual solids level will be limited by viscosityxe2x80x94a solids level that would interfere with efficient handling of the material should be avoided. Otherwise, the solids level should be chosen to supply a sufficient amount of the dual adhesive and surface active agent to bind the guar coating.
In a preferred embodiment where the 2000-3000 molecular weight polyacrylate (e.g., Spinks 211) is used in an aqueous solution, the dual adhesive and surface active agent will be used at a concentration level of about 43%-45% by weight solids, assuming that the guar is present in the preferred range set out below. From about 1% to 5% by weight of this solution should be used, based on the weight of the granules.
The level of guar used in coating these granules will be at least about 1% to 7% based on the weight of the granules previously coated with the dual adhesive and surface active agent. Preferably, the guar will be used at a level of about 2% to 4% percent by weight. Furthermore, it is not necessary to coat all of the cellulosic particles in order to achieve the near instantaneous clumping made possible by the present invention. Indeed, while it is preferred that up to 100% of the granules are coated as little as 25% by weight of the granules may be coated and preferably at least about 50% to 75% by weight of the granules will be coated to achieve the desired clumping speed and hardness.
This improved cellulosic absorbent may also include anti-microbial agents, fragrances and coloring agents. In the discussion above and that which follows, substrates containing at least 10% by weight cellulosic content are referred to as xe2x80x9ccellulosic particlesxe2x80x9d. However, it is preferred that the cellulosic particles used in the practice of this invention contain at least 40% by weight cellulosic content and most preferably at least 50% by weight cellulosic content.
The present invention also entails unique processes for making and using the above cellulosic particles.